I didn't have a proper 6mm spring and I found the recess too shallow and wide for the only ones I had on hand, ball point pen springs (5mm x 25).....so, some reverse engineering and 20 minutes of printing.
this is what happens when engineers get bored.
kudos to wariwasp for their initial design: https://www.thingiverse.com/thing:4791238 (original STLs of files included for completeness only)
same conditions as wariwasp's original posting... NON COMMERCIAL USE ONLY
printing one or two for your friends is cool but please don't sell prints or include it in blasters for your shop unless you have contacted me beforehand so we can try to work something out. I am very reasonable.